Biphase mark encoding is a commonly used format for transmitting data. Using biphase mark encoded data, synchronization or clock data may be extracted from the data without requiring separate transmission of a clock signal.
Several standards use biphase mark encoding. For example, the Audio Engineering Society (AES) has set forth a standard format for biphase mark encoding of digital audio signals often referred to as AES-3. This standard is defined in a document called “AES Recommended practice for digital audio engineering—Serial transmission format for two channel linearly represented digital audio data.” An example form of an AES-3 signal is described in more detail below. The AES-3 specification applies to signals sent over balanced twisted-pair cabling. A similar encoding of digital audio signals is used in SPDIF (Sony Philips Digital Interface).
Under AES-3, actual data rates may be variable. Different systems may have different fixed data rates and one system may use multiple data rates over time. Therefore, conventional designs for AES-3 receivers use analog phase-locked loops to recover clock, data and audio sample synchronization signals. Less expensive digital designs for AES-3 receivers generally have been limited to a receiving input signals having a single, fixed frequency, making them inapplicable to environments in which variable data rates are actually used.
As with most clocked data signals that are transmitted, jitter may arise due to a variety of factors. This prospect of jitter introduction limits, for example, the length or other characteristics of a transmission medium that may be used. Any clock and data recovery scheme should take into account the possibility of jitter that has been introduced in the received signal.